1. Field of the Invention
The present invention relates to a support mechanism for detachably supporting a fixing unit (fuser unit) or other functional units of an image forming apparatus, such as a copy machine, inside the apparatus, as well as to an image forming apparatus employing such a support mechanism.
2. Description of the Related Art
A copy machine, a conventionally known example of an image forming apparatus, works as follows. As shown in FIG. 5, an original document (not shown) placed on platen glass 21 is scanned by an optical unit 22 to produce a latent image corresponding to an image on the document on a photosensitive drum 23. A developing unit 24 convert the latent image into a visual image through an electrostatic process.
The visual image thus produced is transferred onto a sheet of copying paper (not shown) fed from a paper cassette 25 and fused, or fixed, onto the copying paper by a fuser unit 26. A final copy is then discharged from the copy machine. During execution of overall image forming process mentioned above, a fan (not shown) provided on one side of a housing 27 of the copy machine is run to prevent temperature increase inside the housing 27.
Referring to FIGS. 5 and 6, the fuser unit 26 is constructed such that a pressure roller 31 supported by a bracket 30 is pressed by an elastic pushing force exerted by a coil spring 32 against a fuser roller 29 rotating in a frame 28. Surfaces of the fuser roller 29 and the pressure roller 31 are securely pressed against each other in this fashion.
In this construction, the pushing force of the pressure roller 31 exerted against the fuser roller 29 is regulated by varying the amount of displacement of the coil spring 32. Specifically, the amount of displacement of the coil spring 32 is changed by varying the amount of its elastic deformation (compression and extension) by turning a screw 34 fitted in a base plate 33 provided at the bottom of the frame 28 in an appropriate direction. Japanese Laid-open Patent Publication No. S64-80979 and Japanese Laid-open Utility Model Publication No. S62-4770, for example, disclose fuser units constructed as described above.
The conventional fuser unit of the aforementioned construction, however, has a problem that its assembling efficiency and maintainability are poor and it is difficult to visually identify the screw 34 which is used as an operating device, because it is so small and positioned at the bottom of the base plate 33.
On the other hand, Japanese Laid-open Patent Publication No. H5-341688 discloses an image forming apparatus employing a method of regulating a pushing force of a pressure roller exerted against a heating roller by moving up and down a fixture which is held in contact with an end surface of an operating device formed in the shape of a helical cam surface and provided at a lower side portion of a frame by turning the operating device in an appropriate direction, thereby varying the amount of displacement of a coil spring supporting both ends of a frame of a fuser unit upward.
According to this construction, it is possible to manipulate the operating device from outside as it is exposed to the exterior of the apparatus on one side surface of its housing and, therefore, maintainability of the fuser unit in regulating its pushing force is improved due to improvements in visibility of the operating device and its operability.
The aforementioned method of regulating the pushing force of the pressure roller proposed in Japanese Laid-open Patent Publication No. H5-341688 carries a risk of degrading print quality. This is because part of the operating device is exposed to the exterior of the apparatus and, therefore, an operator may inadvertently turn the operating device, thereby causing an unintended change in fixing conditions.
As a result of a recent reduction in size and growing demand for personal use of image forming apparatus as well as a tendency to implement modular design, manufacturers have started to market image forming apparatus incorporating customer replaceable units (CRUs) to meet customer requirements for a higher serviceability ratio and a reduction in down time. This CRU design concept permits customers to replace individual units (CRUs) by themselves without the need to ask for servicing by qualified personnel.
In the design of the image forming apparatus which are expected to be used in the aforementioned fashion, attention should be paid not only to ease of installation and adjustment of the fuser unit but also to methods of installation and fixing of an image forming unit and other functional units. More specifically, due consideration should be given to ease of installation and safety as well as to visibility of operating devices for securing the individual functional units and reliability of the image forming apparatus after installation of the individual functional units.
In view of the foregoing, it is an object of the invention to provide such a support mechanism for detachably supporting functional units including an image forming unit in an image forming apparatus that makes it possible to design the functional units as modularized customer replaceable units (CRUS) and offer enhanced ease and safety of installation work together with improved operability and visibility of an operating device for securing the individual functional units as well as reliability after installation of the functional units. It is another object of the invention to provide an image forming apparatus employing such a support mechanism.
According to the invention, a support mechanism for detachably supporting a functional unit in a connection bay formed in a housing of an apparatus includes a base plate for supporting the functional unit, an operating device which is provided on the bottom of the base plate and can be freely turned, a threaded shaft provided as an integral part of the operating device, a threaded hole formed in the bottom of the functional unit to allow the threaded shaft to be screwed in to secure the functional unit to the base plate, and a biasing member elastically forcing the threaded shaft toward the threaded hole. The base plate detachably supports the functional unit all the way between an exposed position where the functional unit is separated from and drawn out of the connection bay such that the functional unit is exposed to the exterior of the housing and an accommodated position where the functional unit is fitted in the connection bay. The biasing member biases the threaded shaft through the base plate such that a far end of the threaded shaft is guided toward the threaded hole, and the operating device is hidden inside the housing of the apparatus when the base plate is set to the accommodated position.
In the earlier-mentioned conventional fuser unit, part of the operating device is exposed to the exterior of the apparatus and, therefore, an operator may inadvertently turn the operating device, thereby causing an unintended change in fixing conditions and eventually resulting in degradation in print quality. Accordingly, it has conventionally been desired to solve this problem. Especially when it is intended to make an image forming unit, or other functional unit, customer replaceable, due consideration should be given to the efficiency and safety of installation work, visibility of the operating device for securing the unit, as well as reliability after installation of the unit.
In the aforementioned construction of the invention, the far end of the threaded shaft is biased by the biasing member toward the threaded hole formed in the bottom of the functional unit when the functional unit is placed on the base plate drawn out to the exterior of the housing of the apparatus. Therefore, the threaded shaft can be securely fitted into the threaded hole by simply turning the operating device, making it possible to fix the functional unit to the base plate with enhanced ease and reliability.
Also, installation of the functional unit can be easily finished by pushing in the base plate into the housing of the apparatus, thereby joining the functional unit to the connection bay. Also, the base plate can be easily drawn out of the housing, thereby disconnecting the functional unit from the connection bay at the same time, and the functional unit can be removed by just turning the operating device whenever necessary. This construction enables implementation of the CRU design concept, facilitating maintenance by the user.
Since the operating device is hidden inside the housing of the apparatus when the functional unit is pushed into the housing, no user intervention to the operating device occurs during the operation of the apparatus. This serves to prevent system failures or malfunction due to inadvertent manipulation of the operating device and keep the functional unit installed in position in a stable manner, thereby enhancing the reliability of the apparatus.
Furthermore, since the peripheral part of the operating device extends outward beyond the side surface of the functional unit, the user or servicing personnel can easily distinguish the operating device from above when the functional unit has been drawn out of the housing of the apparatus. The enhanced visibility of the operating device serves to improve labor efficiency in maintenance work.
These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description along with the accompanying drawings.